This invention relates to a nanocomposite material, a method for the preparation of a nanocomposite material and to a shaped article of a nanocomposite material.
Over the past decades, it has already been frequently proposed to improve the properties of polymeric materials by incorporating a certain amount of a clay in those materials. The presence of a clay in a polymeric material is beneficial particularly to properties such as the mechanical strength and the heat resistance of the polymeric material.
To thus obtain a nanocomposite material that has the desired properties, it is important that the clay be dispersed in the polymeric material sufficiently homogeneously. This is not easy because the clay and the polymeric material are of a highly different nature. Polymers constitute a normally non-polar, organic material, whereas the clay is a much more polar, inorganic material. Due to this difference, the materials exhibit poor miscibility with respect to each other; they are intrinsically non-miscible. In the literature, it has been proposed first to modify the clay in different ways before it is mixed with a polymeric material. It has also been proposed to modify the clay and then to mix it with a monomeric material, which is thereupon polymerized in the presence of the clay.
In U.S. Pat. Nos. 4,889,885 and 4,810,734, it is described how a cationic clay is first modified with a swelling agent, which increases the interlayer distance of the clay structure. Used as swelling agents are surfactants, with a head group formed by an ammonium, pyridinium, sulfonium or phosphonium group, and one or more non-polar tails. The cationic head group of the surfactant is exchanged with cations between the crystalline layers of the clay and the tails should be compatible with the polymeric material. Then the modified clay is mixed with monomeric material, which can enter into a bonding interaction with the tails of the swelling agent. When, finally, the monomeric material is then polymerized, the polymers are formed between the layers of the clay and a nanocomposite material is obtained.
A disadvantage of these known nanocomposite materials is that the quality of the end product is very highly dependent on the quality of the clay used. Cationic clay is virtually always a natural product, which is not homogeneous in composition. This inhomogeneity of the clay leads to inhomogeneities in the composition of the nanocomposite material, which means that the desired properties are not always achieved in a sufficient quality. It is therefore desirable to make it possible to incorporate into polymeric material a kind of clay that has a better controllable quality and composition.
U.S. Pat. No. 5,658,653 describes a polymer composite comprising a polymeric matrix in which a filler is incorporated. The polymeric matrix can be a polyolefin, polystyrene, polyurethane, epoxy resin, polyimide, polyacetal, polyester, polyvinyl, polyether or polyacryl. The filler is a mixed metal hydroxide that satisfies a specific formula.
In order to enhance the compatibility of the polymeric material and the filler, the surface of the filler has been modified in that particular groups have been provided thereon. These groups can be, for instance, organic acids, salts of sulfonic acids or phosphonic acids. It is also possible that anions of the filler have been exchanged with groups that form hydrogen bridges with the polymeric matrix.
A disadvantage of the material described in the above U.S. patent specification is that the filler is not homogeneously dispersed in the polymeric matrix. This inhomogeneity is presumably due to the fact that only the